Conventionally, in an electronic device with an imaging function, such as a digital still camera or a digital video camera, for example, a solid-state image capture element, such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image sensor is used. The solid-state image capture element has a pixel in which a photodiode (PD) that performs photoelectric conversion and a plurality of transistors are combined, and an image is constructed on the basis of pixel signals output from a plurality of pixels arranged in an image plane on which an image of a subject is formed.
In general, in a CMOS image sensor, imaging is sequentially performed by a rolling shutter method for reading charges generated in a PD for each row on which pixels are arranged.
In contrast, in recent years, there has been developed a CMOS image sensor which has a structure having a memory unit that temporarily holds, in a pixel, charges generated in a PD and performs imaging by a global shutter method for realizing simultaneous charge storage by concurrently transferring the charges from the PD to the memory unit.
Meanwhile, in the CMOS image sensor of a structure to perform imaging by the global shutter method, in order to capture a moving image having no interruption, it is necessary to store charges in the PD and hold the charges in the memory unit in parallel. Therefore, during capturing of a moving image, in order to suppress blooming from the PD to the memory unit, it is preferable to form a lower potential of an overflow gate for overflowing charges generated larger than a stored charge amount of the PD.
On the other hand, during capturing of a still image, it is not necessary to store charges in the PD and hold the charges in the memory unit in parallel, and thus it is not necessary to form a path for overflowing charges from the PD.
Therefore, a configuration suitable for capturing a moving image in which the potential of the overflow gate is formed low is not suitable for capturing a still image. That is, in view of the entire imaging system, it is necessary to reduce the potential of the overflow gate, and as a result, a stored charge amount of the PD decreases.
Accordingly, the applicant of the present application suggests a solid-state image capture element capable of switching of a potential of an overflow gate between a still image and a moving image (see e.g., Patent Literature 1).